JIM LEHRER: Next tonight, an update of the president's promise to shut down the Guantanamo Bay prison. Margaret Warner begins with some background.
MARGARET WARNER: It was a promise President Obama campaigned on, to close the detention center at the U.S. naval base in Guantanamo Bay, Cuba. And on his second full day in office, Mr. Obama signed an executive order to make good on the pledge.
U.S. PRESIDENT BARACK OBAMA: Guantanamo will be closed no later than one year from now.
MARGARET WARNER: But it's proven harder than expected to stick to that timetable.
ROBERT GATES, secretary of defense: It's going to be tough.
MARGARET WARNER: Yesterday, Defense Secretary Gates conceded the deadline may slip.
ROBERT GATES: I was one of those who argued for a firm deadline, because I said that's the only way you move the bureaucracy in Washington. And if you have to extend that date, if at least you have a strong plan showing you're making progress in that direction, then it shouldn't be a problem to extend it. And we'll just see whether that has to happen or not.
MARGARET WARNER: Today, White House spokesman Robert Gibbs said the administration is still working hard to close the base.
ROBERT GIBBS, press secretary, White House: We're not focused on whether or not the deadline will or won't be met on a particular day. Obviously, we've still got work to do, work that's progressing, in reforming military commissions and in locating a permanent detention facility for those that would remain.
MARGARET WARNER: All told, some 800 terror suspects captured overseas have been held at the Guantanamo facility since 2002. There were 240 detainees in January when Mr. Obama took office. And since then, 17 more have been released, including three sent to Yemen and Ireland this past weekend.
Dozens more are believed to have been approved for release and resettlement, but it's been hard to find countries willing to take them. And in Congress, there's been opposition to resettling those detainees on the U.S. mainland or transferring others to prisons here.
On Sunday, Democratic Senator Dianne Feinstein of California debated the issue with Republican Kit Bond of Missouri.
SEN. DIANNE FEINSTEIN, D-Calif.: I know that there are maximum-security prisons from which no one escapes in the United States, which are isolated from neighborhoods.
SEN. KIT BOND, R-Mo.: We don't want to put them in our general prison population where they have and will radicalize other prisoners.
MARGARET WARNER: Officials say between 40 and 60 of the detainees could be prosecuted in either military or federal criminal court. This group includes Khalid Sheikh Mohammed, the accused 9/11 mastermind, and four alleged followers.